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J M Pollok

Publications and source records attributed to J M Pollok.

15 recordsLinked to original sources
PubMed1999

Long-term differentiated function of heterotopically transplanted hepatocytes on three-dimensional polymer matrices.

Hepatocyte transplantation using porous matrices is under investigation as an alternative therapy for certain liver diseases. For this purpose, long-term function of transplanted hepatocytes is mandatory. This problem has not been sufficiently investigated yet. In this study Lewis rats were used as donors and recipients. Stimulated (group A, portocaval shunt) or unstimulated (group B) hepatocytes were transplanted into prevascularized polyvinyl-alcohol matrices. Cell-free matrices served as controls (group C). Matrices were harvested between 1 h and 1 year after implantation and analyzed by morphometry; albumin RNA in situ hybridization; and cytokeratin-, actin-, desmin-, and macrophage-specific antigen immunohistology. The hepatocyte number significantly decreased within the first week following implantation. Between 1 month and 1 year after transplantation a significant increase in hepatocyte number was noted in groups A and B. Albumin transcripts of transplanted hepatocytes were at normal levels at all times except for group B after 1 year. The immunohistology suggested engraftment of nonparenchymal liver cells. We conclude that 3-dimensional matrices provide a sufficient environment for long-term engraftment of transplanted liver cells. The hepatocytes are able, despite suboptimal initial engraftment, to repopulate the scaffold for at least half of the recipient's life span and maintain cell-specific function after sufficient stimulation.

Animals↗
PubMed1999

Is there an optimal concentration of cotransplanted islets of Langerhans for stimulation of hepatocytes in three dimensional matrices?

BACKGROUND: Hepatocyte transplantation using three-dimensional matrices is under investigation as an alternative therapy for several liver diseases. For sufficient transplantation results hepatotrophic stimulation is necessary. We investigated the stimulatory effect of cotransplanted pancreatic islets in different ratios. METHODS: Lewis rats were used as donors and recipients. A portocaval shunt (group A) or sham operation (groups B-G) was performed 1 week before hepatocyte transplantation. Four polyvinyl-alcohol matrices each containing 1.25 x 10(7) hepatocytes (groups A and B) or 1.25 x 10(7) hepatocytes and 125 (C), 250 (D), 500 (E), or 750 (F) islets were implanted between small bowel mesenteric leaves. In group G, medium soaked matrices were implanted. One month after implantation, specimens were harvested and investigated using albumin-RNA in situ hybridization, and insulin, glucagon, and bromodesoxy uridine immunohistochemistry. The hepatocyte area was assessed using image analysis. RESULTS: Hepatocyte area and proliferation ratio increased depending on the number of cotransplanted islets with a peak at 40 islets per 1 million hepatocytes (group E). Cotransplantation of islets in higher concentrations did not further increase hepatocyte area or proliferation ratio. Hepatocytes in all groups expressed albumin RNA at normal transcription levels as compared to standard liver sections. Islets displayed insulin and glucagon in physiological distribution. DISCUSSION: Three-dimensional matrices provide a sufficient environment for transplanted hepatocytes and islets. The hepatotrophic effect of cotransplanted islets is comparable to portocaval shunting and has a saturation limit at 40 islets per 1 million hepatocytes. For further application of islet cotransplantation, this ratio seems to be preferable.

Albumins↗
PubMed1999

Long-term insulin-secretory function of islets of Langerhans encapsulated with a layer of confluent chondrocytes for immunoisolation.

Islet transplantation is a potential cure for diabetes mellitus. The major problem for broad clinical application remains the prevention of transplant rejection without major side effects. Immunoisolation is an experimental strategy to prevent rejection by separating the transplanted cells from the host immune system using a barrier device. Current methods use artificial, not completely inert materials as barrier devices and induce an unwanted foreign-body (FB) reaction. Using the recipients of own cells for encapsulation, the FB reaction could be prevented. This study describes a new method of encapsulation of islets of Langerhans within a capsule of chondrocytes, which may serve as an immunoisolation barrier utilizing the immunoprivileged properties of the chrondrocyte matrix, and demonstrates the functional survival of the encapsulated islets in vitro.

Animals↗
PubMed1999

Heterotopic hepatocyte transplantation utilizing pancreatic islet cotransplantation for hepatotrophic stimulation: morphologic and morphometric evaluation.

Hepatocyte transplantation using three-dimensional (3D) matrices is under evaluation as an alternative therapy for liver diseases. It is known that hepatotropic stimulation optimizes hepatocyte engraftment. We investigated hepatotrophic stimulation by portocaval shunt operation (PCS) or pancreatic islet cotransplantation (ICT) over a period of 6 months. Lewis rats served as donors and recipients, respectively. One week prior to hepatocyte implantation PCS (group A) or a sham operation (groups B-D) was performed. Four polyvinyl-alcohol matrices, each containing 1.25 x 10(7) hepatocytes (groups A and C), 1.25 x 10(7) hepatocytes and 500 islets (group B), or cell-free culture medium (group D, control) were implanted between recipients' small-bowel mesenteric leaves. One, 3, and 6 months after implantation eight polymers from each group were harvested and analyzed by morphometry, PAS reaction, and immunohistochemistry for insulin, glucagon, and bromodesoxyuridine. Morphologically healthy-appearing hepatocytes were found in all cell transplantation groups at all times. Stimulation by either PCS or ICT significantly increased hepatocyte area at 1 and 6 months compared to unstimulated specimens (group C). Over time, an increase in hepatocyte area was noted in all groups. There were no significant differences in proliferation ratios between the three experimental groups. The initially reduced PAS reaction became normal after 3 months. 3D matrices provided a sufficient environment for transplanted hepatocytes and islets. Hepatocytes proliferated and maintained differentiation independent of hepatotrophic stimulation for at least 6 months when 3D matrices were utilized. ICT efficiently stimulated transplanted hepatocytes by means of hepatocyte area. These results justify further research on hepatocyte transplantation and ICT with regard to clinical application.

Animals↗
PubMed1999

Interaction of hepatocytes and pancreatic islets cotransplanted in polymeric matrices.

Heterotopic hepatocyte transplantation (HcTx) in polymeric matrices may become an alternative to liver transplantation for metabolic disorders. Hepatotrophic stimulation by means of a portocaval shunt operation is an established, but invasive, procedure used to optimize hepatocyte engraftment in matrices. We evaluated hepatocyte and pancreatic islet cotransplantation (ICT) as an alternative noninvasive approach to hepatotrophic stimulation. Lewis rats served as donors and recipients. Hepatocytes and islets were isolated using collagenase digestion and seeded into polyvinylalcohol matrices. HcTx and ICT were compared with HcTx plus portocaval shunt and HcTx without stimulation. Matrices were investigated at 1, 3, and 6 months after implantation: the test methods applied were trichrome staining, PAS, immunohistochemistry for insulin, glucagon and incorporated BrdU, and in situ hybridization for albumin RNA. Hepatocytes expressed albumin RNA and formed conglomerates without atypias in all animals. ICT and portocaval shunting increased the number of hepatocytes and BrdU uptake. Alpha cells migrated into the islet-surrounding hepatocytes, whereas beta cells remained immobile. It is concluded that ICT and portocaval shunting supported engraftment of hepatocytes in polymeric matrices equally well. ICT did not interfere with recipient glucose metabolism and did not induce hyperproliferative premalignant foci within the transplanted hepatocytes. The technique is an attractive approach to hepatotrophic stimulation of bioartificial liver equivalents.

Animals↗
PubMed1999

Influence of pancreatic islets on growth and differentiation of hepatocytes in co-culture.

Improvement of cell culture conditions in hepatic tissue engineering may permit cell/tissue banking and the generation of liver tissue equivalents for transplantation. In these systems, continuous hepatotrophic stimulation is still necessary. We investigated the stimulatory effects of pancreatic islets on hepatocytes in co-culture and characterized the stimulatory mechanisms. Hepatocytes and pancreatic islets were harvested from Lewis rats. Cells were cultured on collagen dishes either with nonstimulated media (controls and co-cultures with low or high islet rate) or stimulated media (controls and co-cultures). To characterize stimulatory mechanisms, additional co-cultures with membrane separation, with antiinsulin, antiglucagon, and with both antibodies were examined. Hepatocyte numbers, albumin secretion rate by enzyme-linked immunoadsorbent assay, and monoethylglycinxylidid biotransformation values by fluorescence polarization immunoassay were assessed. A radioimmunoassay measured insulin and glucagon concentrations. In groups with nonstimulated media, cell number was higher in co-cultures with low islet rate, and albumin secretion rate was increased in co-cultures with high islet rate compared to controls. MEGX biotransformation was decreased in co-cultures. In groups with stimulated media, co-culture had no impact on cell number or albumin secretion rate. Hepatocyte numbers and albumin secretion rates were not changed in co-cultures after membrane separation. Islet effects on hepatocytes were reduced in co-cultures with antiinsulin, antiglucagon, or both antibodies. Pancreatic islets provide stimulation for hepatocytes in vitro. Islet effects were mediated by soluble factors, and are dependent on insulin and glucagon. These results permit further investigations towards three-dimensional transplantable hepatocyte-islet devices for continuous in vitro and in vivo stimulation.

Albumins↗
PubMed1998

Formation of spheroidal aggregates of hepatocytes on biodegradable polymers under continuous-flow bioreactor conditions.

Our laboratory has investigated heterotopic hepatocyte transplantation on biodegradable polymer matrices as an experimental treatment for end-stage liver disease. One of the limitations has been survival of sufficient cell mass after transplantation. We hypothesize that in vitro conditioning of cells within polymer matrices prior to implantation may increase hepatocyte survival and function. In this preliminary study we investigated the effect of continuous flow on hepatocytes and sinusoidal endothelial cells on poly-L-lactic acid (PLLA) discs in vitro. Highly porous PLLA discs were manufactured measuring 18 mm diameter by 1 mm thickness using previously described techniques. Hepatocytes were isolated from adult, male Lewis rats (200-300 g) using a two-step collagenase digestion. Sinusoidal endothelial cells were isolated using a two-step collagenase digestion, differential sedimentation, Percoll gradient centrifugation, and selective adherence. PLLA discs were seeded with hepatocytes alone or with co-cultures of hepatocytes and sinusoidal endothelial cells. Seeded discs were then secured within a flow bioreactor chamber and exposed to continuous flow of culture media at a rate of 20 ml/minute through the chamber. Seeded discs placed in static culture conditions served as controls. Specimens seeded with only hepatocytes were harvested at 24 hours, 48 hours, and 168 hours after seeding. Co-culture specimens were harvested after 168 hours. Specimens were viewed under phase-contrast microscopy and then formalin-fixed and prepared for histologic sectioning. Sections were stained with Hematoxylin and Eosin and then analyzed with light microscopy. Hepatocytes under flow conditions formed spheroidal aggregates of cells of 50 to 200 microns in diameter by 24 hours in culture. Hepatocytes in static conditions showed decreased aggregation of cells and spheroid formation was absent. Co-cultured specimens under flow also showed spheroid formation with endothelial cells lining the outside of hepatocyte spheroids. Co-cultured specimens in static culture showed no spheroid formation and no organization between sinusoidal endothelial cells and hepatocytes. These results suggest that continuous flow increases organization of hepatocytes cultured within biodegradable polymer matrices.

Animals↗
PubMed1998

[Immuno-isolation of xenogenic islands of Langerhans in a tissue engineered autologous cartilage capsule].

Islet transplantation is a potential cure for diabetes mellitus. The major problem for clinical application remains the prevention of transplant rejection without major side effects. Broad application in early disease will make the usage of xenogeneic tissue necessary. Immunoisolation is an experimental strategy to prevent rejection, by separating the transplanted allogeneic or xenogeneic cells from the host immune system using a barrier device. Current methods of immunoisolation use artificial, not completely inert materials as barrier devices and induce an unwanted foreign body reaction. Using recipient own cells for encapsulation the foreign body reaction could be prevented. This study describes a new method of encapsulation of islets of Langerhans within a capsule of chondrocytes, which may serve as an immunoisolation barrier utilizing the immunoprivileged properties of the chondrocyte matrix and demonstrates the functional survival of the encapsulated islets in vivo.

Animals↗
PubMed1997

The effect of donor and recipient age on engraftment of tissue-engineered liver.

A novel treatment for end-stage liver disease using heterotopic hepatocyte transplantation on biodegradable polymers has been investigated. Survival and repopulation of adequate cell mass to replace hepatic function has been the principal difficulty of this method. Hence the authors have begun to investigate the role of donor and recipient age on the efficiency of hepatocyte transplantation. Lewis rats were used as donors and recipients. Hepatocytes were isolated with a collagenase digestion, both for the adult and fetal livers (17 days estimated gestational age). After digestion, the hepatocytes were seeded onto 95% porous poly-(L)-lactic acid matrices. The polymer-cell constructs with adult or fetal cells were then implanted between mesenteric leaves of three different recipient groups: adults (approximately 200 g), 2-week, and 4-week neonates (two to five animals per group, depending on litter size). The specimens were harvested at 4 weeks, stained with Hematoxylin and Eosin (H&E), and the cell area of each specimen (24 sections per group) was quantitated using morphometric analysis. Results were statistically analyzed using an unpaired, two-tailed Student's t test. At 4 weeks, all specimens showed survival of groups of hepatocytes, especially along the periphery of the polymers and near blood vessels. The hepatocyte cell area for the six groups was calculated in square micrometers: the adult cells transplanted into adult recipients, 0.16 x 10(5) microns2; fetal cells into adults, 0.47 x 10(5) microns2; adult into 4-week neonates, 1.17 x 10(5) microns2; fetal into 4-week neonates, 4.54 x 10(5) microns2; adult into 2-week neonates, 2.98 x 10(5) microns2, and fetal into 2-week neonates, 5.81 x 10(5) microns2. In all three recipient groups, the area of fetal hepatocytes was approximately two to three times the area of the adult hepatocytes (P < .05 for 2-week and 4-week neonatal recipients, P = .06 for adult recipients). Also, as the recipient age decreased, there was an increase in the hepatocyte cell area (P < .05 for fetal or adult groups). The authors conclude that fetal hepatocytes heterotopically transplanted have a significant survival advantage over adult hepatocytes, independent of recipient age. The authors further conclude that the neonatal environment is more favorable than the adult environment for implantation of hepatocytes.

Age Factors↗
PubMed1997

[Complicated amebic liver abscess--course and therapy].

We report on a case of an amoebic liver abscess acquired during a holiday in Bali. Transdiaphragmatic migration and consecutive atelectasis of the right lung caused respiratory insufficiency, requiring immediate surgical intervention. Complications consisted of massive bleeding into the colon concomitant with a reactivated CMV-infection. In addition, toxins of Clostridium difficile and enterohaemorrhagic E. coli were seen in the faeces. In contrast to the majority of uncomplicated cases of amoebic liver abscess, usually treated with amoebicidal drugs only, surgical intervention was clearly indicated in our patient.

Combined Modality Therapy↗
PubMed1996

Tissue engineering.

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Current treatment modalities include transplantation of organs, surgical reconstruction, use of mechanical devices, or supplementation of metabolic products. Tissue engineering is the application of the principles and methods of engineering and the life sciences to the fundamental understanding of structure/function relationships in normal and pathological tissues and the development of biological substitutes to restore, maintain, or improve function. This article discusses the challenges of this interdisciplinary field and its attempts to provide solutions to tissue creation and repair.

Artificial Organs↗